In recent years, techniques for designing micrometer sized structures in electrical, optical and photonic applications have been developed. Such techniques may be based on molding and contact printing, collectively referred to as soft lithography.
Soft lithography typically makes use of a patterning device, such as a stamp comprising a transfer surface having a well defined relief pattern. Structures and features are formed upon conformal contact between the stamp transfer surface and a substrate.
In order to pattern large areas using soft lithography techniques, it is crucial that no deformation of the patterns occurs when the stamp is handled. Furthermore, it is critical that the stamp conforms to the “non-flatness” or roughness of the substrate. The characteristics of the stamp material are thus of special importance and may be critical.
Commonly used stamp materials include poly-di-methyl siloxane (PDMS) based materials, e.g. Dow Comings Sylgard 184. Although such materials are capable of establishing reproducible conformal contact with a substrate material, they are subject to problems associated with pressure induced deformations when providing very small pattern features in the nanometer range, e.g. in the sub 100 nm range. Moreover, conventional PDMS materials are susceptible to rounding of sharp corners due to surface tension, especially when features smaller than 100 nm are molded.
One way to increase the stability of stamp materials is to increase the Young's modulus; i.e. elasticity modulus of the material. However, an increase in Young's modulus may result in that the material becomes too rigid, resulting in poor accommodation onto rough and non-flat surfaces. Hence, soft lithography is limited in resolution by the stamp material used, and for large area imprint the material needs to have a Young's modulus being high enough to generate stable features having very small dimensions, but at the same time the material must be as soft as possible to accommodate conformal contact on rough and non-flat substrates.
WO 2007/121006 discloses compositions and methods that may be used to form low thermal distortion molds. The compositions comprise a curable elastomeric silicone composition formed using a de-volatized polymer and at least one de-volatilized cross-linker. In one embodiment, the silicone composition comprises a silicone resin and an organosilicon compound having an average of at least two silicon-bonded hydrogen atoms per molecule and a catalytic amount of a hydrosilation catalyst.
A drawback in using silicone resins in transfer layers for lithographic purposes is that resins are glass like with glass transitioning temperatures ranging from room temperature to 300-400° C. The Young's modulus of such resin materials is very high (above 100-200 MPa), which may prevent conformal contact, as the stamp cannot follow the micrometer and even nanometer sized roughness of a substrate. The imprinted layer forms a rigid material, and removing the stamp requires high forces. This results in that the forces on the features in the stamp and imprinted features become very high, which may result in damage of the stamp and/or the imprinted features.
Accordingly, there is a need in the art to provide a material to be used in imprint lithography of large areas, said material being capable of providing patterns of nanoscale structures having high fidelity and good mechanical robustness while maintaining good conformal contact on rough and non-flat substrate surfaces.